There have been recent numerous reports of accumulations of mutations in the mitochondrial genome in a variety of human diseases and with age. It has been proposed that these mutations may be due in part to the mitochondrial oxidative pathways which provide most of the cell's energy in the form of ATP but generate potentially hazardous free radicals in the process. To examine for the occurrence of mitochondrial mutations in the central nervous system, we have amplified and sequenced regions of the mitochondrial genome from CNS tissue obtained from individuals of varying ages. In one study, we sequenced 32,000 base pairs of mitochondrial DNA cloned from retinal tissue from a 71 year old individual. This approach revealed only one heterotypic mutation. A second study evaluated mitochondrial DNA isolated from human brain tissue by widely spaced PCR analysis. This technique employs distant PCR primers and PCR conditions optimized to amplify DNA harboring large scale deletions. Large mitochondrial DNA deletions were detected in increasing amounts in individuals over 27 years of age. The laboratory plans to investigate the significance of these deletion mutations and their relationship to the aging process and disease states.